BPM

bio

by new to pace.... - 2023-09-29 16:51:19

It would help to answer your query if you filled in your bio with at least the make, model and your location.  As sometimes are answers to you are different based on the make and your location.

new to pace 

How were you measuring your HR?

by crustyg - 2023-09-29 18:34:01

If you were accurately measuring your HR with palpation and a watch, then your PM or leads need attention.

If you were relying on a smart watch then this is quite common, they aren't very reliable at measuring HR, especially if not snug enough.

I know my device is working 100% correctly: during a gym session yesterday, my Garmin Swim II was claiming a HR of 45BPM (my lower limit is 50BPM).  I tightened the strap one notch and suddenly my watch showed 50BPM.

Ectopic beats?

by Gemita - 2023-09-30 03:58:12

RZ:  Your comment, “I feel fine once I get up to speed" is quite telling.  I am sure your doctors will be more interested in any symptoms you might be getting when you notice heart rate falls.  Your symptoms/Lower Rate Liimit drops could point to heart rhythm disturbances, like ectopic beats?  The cup of coffee and “getting up to speed” probably raised your heart rate which helped to outpace any irregular, pausing, premature atrial or ventricular heart beats and by doing this, you felt better.  

There have been several posts lately about whether our pacemakers always prevent our heart rate from falling below our Lower Rate Limit?  This is a fair question to ask, especially when members can be so symptomatic and may even collapse or feel close to collapse with their poorly controlled irregular heart rhythms.

When doctors review my pacemaker data (electrograms/rate histograms) they sometimes see paced or sensed atrial or ventricular rates below the programmed Lower Rate Limit.  I didn't fully understand the information given to me at the time, but I will share nonetheless.  I was advised that these “slow” rates can be due to programmed features or sensing algorithms.  Atrial and/or ventricular rates below the Lower Rate Limit for example can be the result of over-sensing or caused by:

Rate Hysteresis - a programmable feature that allows the pacemaker to begin ventricular pacing only when our own intrinsic heart rate falls below the set Rate Hysteresis.  If the lower pacing rates are the result of Rate Hysteresis and these cause symptoms, doctors can adjust this setting or programme the Rate Hysteresis feature OFF.

A-V conduction during paced A-V function.  A-V conduction can delay ventricular pacing. If a patient is paced at or near the Lower Rate Limit in both the atrium and the ventricle, and an atrial paced event is intrinsically conducted to the ventricle, it may cause the next V-V interval to be extended beyond the programmed Lower Rate Limit.  

Premature Ventricular Contractions (PVCs) - there is a protective on/off detection safety mode since a PVC can reset pacemaker cycle timing and delay atrial pacing.  

It is complex and I am only beginning to understand some of this, but I hope I have given some examples above of how our Lower Rate Limit could be affected by settings, heart rhythm disturbances or perhaps by other factors beyond our control?  I agree with crustyg that our home monitors may give unreliable results, but if you are consistently getting difficult symptoms and noticing heart rate drops, I would perhaps ask your doctors for some additional monitoring/pacemaker checks. 

rest mode/sleep rate/night rate/hyseresis

by Selwyn - 2023-09-30 10:54:30

Some pacemakers have a REST MODE setting ( this can be turned on and off). The rest mode will function, if for instance you are prone for 20 minutes with little movement. As soon as you get up the rest mode is turned off and then the lower limit BASE RATE comes on ( 60 bpm for yourself).

The Rest Mode is used to save the battery ie. to increase your pacemaker longevity. 

The St Jude pacemaker's rest mode is activity based

Medronic and Biotronik are time based ( learnt from your activity pattern)

Boston Scientific is hyperesis based ( ie. it gives you the chance to slightly over-ride the programming so that if possible your own intrinsic  heart rate can take over- as Gemita says above. Hysterein (Greek)=to be late - ie. the programme introduces a delay to give your own rate a chance to function).

I don't think you need worry. Yes, you can be paced below your base rate when you have active your sleep settings.

( Interestingly enough, my hearing aids do the same and switch themselves off if I have an afternoon snooze!).

Gemita - Oversensing

by Penguin - 2023-09-30 17:11:44

'I was advised that these “slow” rates can be due to programmed features or sensing algorithms.  Atrial and/or ventricular rates below the Lower Rate Limit for example can be the result of over-sensing'

May I ask about this? Hopefully my Q is relevant to the OP.

How does over sensing cause h/rates below the LRL?  Any chance of an explanation - apologies if it's too big an ask. 

Selwyn

I was wondering how much you know about the rest rates on St Jude / Abbott PMs.  Any idea how low the rest rate might be and whether or not it is programmable or a standardised reduction? 

We don't know which brand of PM the original poster has, but her rate of 48 bpm is roughly 20% lower than her LRL of 60 bpm.   Is a 20% reduction usual? If so this would allow h/rates as low as 40 bpm if an LRL is set to 50 bpm.   

Thanks in advance for any advice offered. 

Penguin

by Gemita - 2023-09-30 19:21:55

My understanding is that oversensing can occur when the pacemaker detects electrical activity that it incorrectly interprets as atrial activity (P-wave) or ventricular activity (R-wave).  

Oversensing can also occur when electrical events in one chamber are sensed by the lead in the other chamber, resulting in inappropriate inhibition of the pacemaker in the latter chamber.  This type of oversensing is called pacemaker crosstalk.

Oversensing may also occur when the ventricular lead interprets the T-wave as an R-wave.

So to recap, oversensing is when the pacemaker senses signals that are not true P-waves or R-waves.  Sensing of such signals normally inhibits the pacemaker.   Oversensing may therefore lead to underpacing and to a reduced lower rate.  I hope that explanation is acceptable to you.  It is the best I can offer after my combined Covid and Flu vaccines today.

Please feel free to give me your interpretation of over sensing?

Gemita

by Penguin - 2023-10-01 03:14:48

Thank you for that Gemita. I can't add anything. Your explanation is far more in-depth than my own understanding of oversensing even though you say that you're not functionning too well after your combined vaccine. (I hope you feel better soon btw).

It seems that over sensing can be very troublesome indeed and can be triggered by muscle movements associated with digesting food / drinking - alcohol and / or fizzy drinks (artifact) and strong emotions rather than the heart itself.  These symptoms and triggers could perhaps be mistaken for an arrhythmia or even trigger an underlying arrhythmia and cause discomfort and distress.  We are reliant on our techs to programme our sensing appropriately. 

I have no idea whether under sensing could also prove problematic?

Re: My Q. to Selwyn. I've taken a look at the available rest rate settings for my PM. 

The rest rate is not an automatic or standard setting - e.g. somebody has to decide whether or not to programme a rest rate which I note can be programmed at heart rates as low as 30 bpm. A patient's day time activity levels would need to be considered as described in their histograms if this setting was switched on, particularly if the rest rate is activated by inactivity as Selwyn describes.  Any other factors influencing a patient's activity levels during the day would also need to be considered.

  It is interesting that a rate as low as 30 bpm is programmable, as there has been much discussion about low heart rates during sleep on this forum recently and I asked the question previously - 'how low is too low' for heart rates at night. Opinions seem to vary. 

Factors which may influence any decision about programming a rest rate might include:  a background of atrial arrhythmia which appears at lower heart rates; pre-pacing night time pauses which higher rate pacing subsequently dealt with; ischaemic type symptoms at night from low heart rates; AVB and programming such as long AVDs. 

There's a lot more to consider than saving battery!

Sensitivity v. Threshold settings

by Selwyn - 2023-10-01 13:51:32

A high  sensitivity, that is over sensitivity  ( ie the ability to be influenced by ECG waves ) = a low threshold ( ie. that level of electrical activity needed to trigger a sensor).

The idea is to adjust the sensitivity ( ie. the inverse is the threshold) so that only the desired waves are sensed ( ususally the R wave in the ECG QRS complex).  Your EP can vary the threshold/sensitivity according to your physiology eg. in my case I have large R waves (the R wave represents mainly left venticular contraction) as I have a hypertrophic cardiomyopathy, some illnesses thin heart muscle and the R wave would be less high). 

Undersensing would mean that the pacemaker is blind with regard to sensing ! You really want synchronised pacing between atria and ventricles so as to avoid pacemaker syndrome. Also as Gemita mentions, there is the question of the sensor picking up waves that it should not do so and the result is a tachycardia.  If we really want to stir things up there are the dreaded 'blanking intervals'!!.

( see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5067035/ for some insight about sensing, Penguin, as requested.)

The rest rate ( sleep)  varies according to the individual's needs. What you don't want is to stand up and go dizzy or faint whilst getting out of bed in the night ( eg. to the toilet). Cardiac output = stroke volume X heart rate.   Setting the resting rate is as much as an art as a science, the aim being to preserve the life of the battery.

The great joy of pacemakers that have automatically adjusing rates based on time is when you travel from say, the UK to New Zealand ( 12 hours time difference). It adds a new dimension to 'jet lag' !

how did you measure this

by dwelch - 2023-10-07 05:07:52

First and foremost where did the 48 come from?  Some watch or other?  Ignore that.  Finger on wrist or neck, full 60 seconds no cheating.  Maybe the led based finger cuffs, I believe in those and they are cheap, but end of the day if it is not what I think it should be, full 60 seconds no cheating.

The device is not necessarily doing a 60 bpm limit on every single or every so many beats, it is averaging that so you may go fast or slow if your natural pacer is trying to be down at or below that range.

Do you have a take home box?  did you press the button? did the office say your pacer recorded something and you need to come in?